This invention is directed to segment rolls for briquetting and compacting presses.
Briquetting and compacting of various materials have been undertaken for many years. Particular problems are presented, however, where briquetting and compacting procedures involve high temperature operations, for example, in the handling of iron ore. High pressures are involved in such processes as well as high temperatures. The maintenance of such pressures at elevated temperatures has resulted in wear problems so that replacement of rolls became necessary in many cases. This represented an expensive replacement operation and, in addition, it was necessary to leave equipment idle for extended periods to provide time for the replacement of the worn equipment.
Equipment has been developed which involves the utilization of roll segments attached to a roll core. Such roll segments are illustrated in U.S. Pat. Nos. 3,077,634 and 3,938,930. With the use of roll segments as described in the aforementioned patents, it was only necessary to replace worn segments when briquetting or compacting materials at elevated pressures and temperatures. These segments were attached in a manner that permitted quick replacement so that the expensive and time consuming task of replacing an entire roll could be eliminated.
Segmented rolls presented difficulties from another standpoint due to the fact that the material being handled often moved between and under the mold segments. This difficulty presented a particular problem when the materials to be formed were of very small article size and where high pressure and temperatures characterized the operation. The heat generated tended to create displacements between the segments and the roll core while the prevailing pressures caused the particulate material to move into spaces developed between displacements.
Attempts have been made to secure the roll inserts or segments in such a manner that they would not be significantly displaced even under the severe thermal conditions. As described, for example in the aforementioned U.S. Pat. No. 3,077,634, the mold segments were provided with diverging end walls and retainer rings were provided with mating surfaces for close engagement with the end walls. These retainer rings were in turn secured to the roll core.
This arrangement was not entirely satisfactory, and this was also true of the arrangement described in the aforementioned U.S. Pat. No. 3,938,930. In this system, shims of a low melting point metal were located between adjacent faces of the mold segments. When elevated temperatures in the order of 450.degree. to 500.degree. C. were achieved, for example, during processing of iron ore, the shims would melt. Upon reaching the shim melting point, in the order of 290.degree. to 370.degree. C., this material would become molten and would be displaced from the gaps between mold segments. This displacement occurred as a result of the expansion of the mold segments due to the temperature rise with the purpose being that the expansion would automatically take up the space previously occupied by the shims. This was intended to ensure the uniform placement and expansion movement of mold segments and thus accurate alignment and at the same time prevent the deposition of material being handled in the expansion gap.
In practice, however, the described arrangement is not effective to avoid this problem. As with the arrangement described in U.S. Pat. No. 3,077,634, the material being handled penetrated between and under the segments causing a loss of close engagement between the segments and the roll seats. This resulted in deformation of the materials, breakage of parts, and similar problems.